Not applicable.
(1) Field of the Invention
The present invention relates to lamp life estimating systems and more particularly to a system for alerting the user of a device or fixture employing an incandescent lamp to the expected time to failure of that incandescent lamp (light bulb). The system may be integrated into a vehicle or may be a stand alone system.
(2) Description of the Prior Art
A common failure mode for incandescent light bulbs is the parting of its filament caused by thermal shock during turn-on. The possibility of this occurring increases as the bulb is used and its filament xe2x80x9cboils offxe2x80x9d, leaving it thinner and physically weaker. Advertised operating life estimates for a bulb tell a user what to expect on average for a useful life. However, mitigating factors such as the frequency of turn-on can alter the useful life expectancy of the bulb and unexpected failures during turn-on and during continuous operation often occur. The basic failure mode remains the same in all cases; the weakening of the filament by the boiling off of the filament material and ultimate parting of the filament. Empirical data derived from a manufacturer""s testing for the life expectancy of their various types of incandescent bulbs can be used as a practical reference point to estimate the expected life remaining for a bulb.
For ordinary home use, expected life remaining may not be critical, but for some situations such as automobile head lamp burn out or burnout of safety lighting in critical areas of a plant or parking lot this can be a safety concern. Knowing how much longer a bulb might last provides a considerable safety factor as well as a financial factor to an auto owner by avoiding being stopped for a moving violation because of a burned out lamp. The safety and financial considerations connected to dependable lighting systems for commercial and municipal properties is also considerable.
Systems for predicting the failure of a lamp are known in the art. For example, U.S. Pat. No. 5,578,998 to Kasprowicz illustrates a lamp failure predicting apparatus which includes a power supply and a resistor in series with an electric lamp. The apparatus further includes a data acquisition system for comparing a voltage drop across the resistor at a predetermined time with a predetermined minimum value. The method employed by Kasprowicz includes the steps of establishing a predetermined minimum value of voltage drop across the resistor for acceptable lamps, placing a test lamp in series with the battery and resistor, and supplying voltage to the test lamp for a test interval of time. The method further includes the steps of determining a voltage drop across the resistor at a predetermined time, comparing the voltage drop with the predetermined minimum value, and rejecting the lamp when the voltage drop is below the predetermined minimum value.
U.S. Pat. No. 5,952,832 to Stevanovic et al. relates to a diagnostic circuit for predicting fluorescent lamp failure by monitoring filament currents. When a filament failure is detected, information is processed and a request is sent to replace the lamp before it actually fails. The diagnostic circuit is low power and low voltage and is electrically isolated from the high voltage end of the lamp.
The detection systems of Kasprowicz and Stevanovic et al. provide testing on operating lamps in order to measure voltage changes. Additionally, they both use complicated and expensive circuitry to accomplish their tasks.
U.S. Pat. No. 4,831,564 illustrates an apparatus for estimating and displaying the remainder of lifetime of a xenon lamp. The apparatus has a memory in which is stored data on the values of the discharge power of an average xenon lamp for maintaining the irradiance of the light emitted from the xenon lamp on the surface of a sample at a predetermined level, and the corresponding time of use of the average xenon lamp; a discharge power measuring device for measuring the level of the discharge power of a xenon lamp being used to irradiate the surface of a sample while the xenon lamp is being controlled to maintain the irradiance of the light emitted from the xenon lamp on the surface of the sample at a predetermined level, a timer for providing at each of a plurality of predetermined times instructions for starting a comparison of the value of the discharge power of the xenon lamp being used with the stored values, an arithmetic unit for obtaining from the memory the value of the stored cumulative time of use corresponding to the measured value of the discharge power of the xenon lamp being used and the value of the limit time of use of the average xenon lamp, and computing the difference as the estimated remainder of the lifetime of the xenon lamp being used; and a display for indicating the estimated remainder of the lifetime of the xenon lamp.
U.S. Pat. No. 5,057,814 to Onan et al relates to an electrical malfunction detection system which has a power supply connected to lamps by a low value resistor. The resistor is part of a voltage divider system which provides input signals to a number of comparators. The comparators provide appropriate signals to a microprocessor to indicate normal operation. When a malfunction is detected, the voltage drop across the low value resistor changes and alters the output of the comparators. The microprocessor thereafter produces an appropriate warning signal. The system is incorporated into a vehicle turn signal circuit to detect a burned out bulb.
U.S. Pat. No. 5,274,611 to Donohoe illustrates an apparatus for estimating the expired portion of the expected total service life of a mercury vapor lamp based upon the time the lamp is electrically energized. The length of time the lamp is energized is measured for each time period that the lamp is energized throughout the life of the lamp. A lamp usage value is determined for each time period that the lamp is energized. The lamp usage value for each time period is determined by assigning a first time dependent value for each time unit of a first predetermined time segment of the time period that the lamp is energized. A second time dependent value is assigned for each time unit of a second predetermined time segment of the time period commencing after the expiration of the first time segment that the lamp is energized. A third time dependent value is assigned for each time unit of the time period that the lamp is energized beyond the expiration of the second time segment. The first, second and third time dependent values are combined to form the lamp usage value for each time period. The lamp usage values are accumulated for each time period the lamp is energized to provide a total of the lamp life usage value. The total lamp life usage value is displayed as an indication of the expired life of the lamp.
U.S. Pat. No. 5,801,623 to Chen et al. illustrates a method of detecting a lamp outage condition in a vehicle flasher system. The method includes the steps of a) initializing an adaptive flasher current variable when the vehicle flasher system is powered; b) monitoring the vehicle flasher system to detect a driver flasher signal request; c) measuring current output from the plurality of lamps in the vehicle flasher system; d) determining whether the level of measured current is indicative of a lamp outage condition by comparing the measured current to the adaptive flasher current variable; e) setting the adaptive flasher current variable equal to the measured current if the measured current falls within a predetermined learning range, thereby compensating for resistance changes in the flasher system over time to allow lamp outage detection; and f) returning to step b).
The Suga, Onan et al., Donohoe, and Chen et al. systems are complex. Further, they either deal with lamps which are in an outage condition already or equipment situations which depend on using running time totals and comparators to predict life expectancy of the items under test.
Accordingly, it is an object of the present invention to provide a system for indicating the estimated remaining life of a light bulb.
It is a further object of the present invention to provide a system as above which is simpler and less complicated.
The foregoing objects are attained by the estimated remaining lamp life indicator system of the present invention.
In accordance with the present invention, a system for estimating the remaining life of a light bulb or lamp broadly comprises means for determining a physical condition of the light bulb or lamp while the light bulb or lamp is in a non-operating mode, means for comparing the physical condition of the light bulb or lamp to a reference physical condition of a light bulb or lamp near the end of its life, and means for displaying an indication of a life expectancy for the light bulb or lamp.
A method for estimating the remaining life of a light bulb or lamp broadly comprises the steps of measuring the cold filament resistance of the light bulb and comparing the measured cold filament resistance to a reference near end of life filament resistance.
Other details of the estimated remaining lamp life indicator system of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.